Flavan salt



U.S. Cl. 260-3452 United States Patent 3,520,905 FLAVAN SALT Calvin K.Johnson, White Bear Lake, Minn., assignor to Minnesota Mining andManufacturing Company, St. Paul, Minn., a corporation of Delaware NoDrawing. Original application Nov. 23, 1966, Ser. No. 596,410. Dividedand this application May 16, 1969, Ser. No. 839,125

Int. Cl. C07d 7/20 1 Claim ABSTRACT OF THE DISCLOSURE Single componentlatent curing epoxy resin composi tions containing as a heat activatablecuring agent a crystalline polyphenate salt of a polyamine and apolyhydric phenol, substantially insoluble in the resin at roomtemperature, preferred examples being a 1:1 salt of 2,4,4-trimethyl-Z',4',7-trihydroxyflavan and N,N'-dimethyl-l,3 propanediamine,andthe 2:1 salt of bisphenol A and triethylenetetramine.

This is a division of application Ser. No. 596,410 filed Nov. 23, 1966.

This invention relates to latent curing epoxy resin compositions.

Mixtures of epoxy resins and conventional amine curing agents generallyhave a short pot life, i.e., remain free flowing and uncured for only ashort time at room temperature. Aliphatic amine curatives, commonlyused, gel the resins within about /2 to 3 hours at room temperature.Considerable eiforts have been devoted to developing epoxy resincompositions containing latent curing agents which will have a long potlife at room temperature, thus improving the convenience of handling andstoring the resin compositions, butwhich will cure rapidly upon heating.For example, boron trifluoride amine complexes have been used as latentcuring agents. See, for example, US. Pat. 2,717,885 (Greenlee) issuedSept 13, 1955. These complexes, however, provide slow cures and arecorrosive sensitive to moisture, and not truly latent due to a gradualrelease of the amine curative from the complex, or cure of the resin bythe complex itself.

Carboxylic acid salts of amines have also been used as latent curatives,but the pot lives of the resin mixtures using the same are short due toesterification of the acid groups by reaction with the epoxy groups.Also, the cure rates provided by these curatives at elevatedtemperatures are slower than those obtained by using the correspondingfree amines. Other latent curing agents have been used such asdicyandiamide and triethanolamineborates, but these require long hightemperature curing cycles to give optimum properties.

The present invention provides epoxy resins containing new latent andsemi-latent curing agents having shelf lives equal to or better thanthose of known latent curing resins which can be activated at lowertemperatures and which, once activated, will cure to hard, tough solidsmore rapidly than latent compositions hitherto available. The normalcuring agents used in this invention are crystalline polyamine salts ofpolyhydric phenols which are substantially insoluble in the resincompositions at room temperature. These curing agents rapidly melt and/or dissolve in the resin upon moderate heating. The curing agents in[finely divided form resist settling in the resin composition so thatthe compositions can be cured in thick crosssections to a substantiallyuniform hardness from top to bottom. The curing agents used in thisinvention often surprisingly provide more rapid cures than thecorresponding unblocked amines. The rate of cure provided by thesecuratives is more rapid than with latent curing agents previouslyavailable. The curatives used in the resin systems of this inventionsubstantially eliminate the problem of dermatitus caused by free aminecuratives. Moreover, the curing agents used in this invention arenon-hygroscopic, non-corrosive, and moisture insensitive, in sharpcontrast with aliphatic polyamines and BF -amine complexes.

Monophenol salts amints have been used as non-latent curatives for epoxyresins. See, for example, British Pat. 959,028 issued May 27, 1964,which proposes the use of ammonium phenates as accelerators in anhydridecured epoxy resins. Such salts, however, are soluble in the epoxy resinsand, although these curatives provide some improvement in pot life, theydo not provide long term latency. The use of amine salts of tar acids ascuratives for epoxy resins is described in South African Pat. 62/ 2043.These phenolamine salts are low viscosity liquids which are soluble inthe epoxy resins and cause them to gel in only a few hours at roomtemperature.

The curatives used in this invention are crystalline dior polyaminesalts of dior polyhydric phenols insoluble in the epoxy resin. Phenolamine salts have also been referred to as phenol amine adducts, phenolamine complexes, and ammonium phenates in the literature. The presenceof strong broad absorption bands in the 3.7 to 4.2 region of theinfrared spectra of these compounds indicates that they are ammoniumphenate salts.

An important advantage of the curing agents used in the resins of thisinvention is that the phenols, which contain two or more phenolichydroxyl groups per molecule, react with the epoxy groups duirng thecure and serve as crosslinking or chain extending agents. Thus thepolyhydric (including dihydric) phenols, when liberated by heating ofthe resin composition, become an integral part of the cured resin, andthus contribute to the ultimate properties of the material rather thanbeing distributed therein in the form of an inert filler which coulddetract from the properties of the resin if present in significantamounts. Any polyphenol which forms crystalline substantiallyresin-insoluble salts with polyamines may be used to prepare the type oflatent, heat activatable curatives disclosed in this invention. Examplesof such phenols are resorcinol, bisphenol A, 4,4'-dihydroxybiphenyl,1,5- dihydroxynaphthalene, 2,4,4 trimethyl-2',4,7-trihydroxyflavan,2,2,4-trimethyl-4-(2,4-dihydroxy-phenol) chroman, and p,p'-oxybisphenol.Other polyhydric phenols are given in the accompanying examples, andmany other polyhydric phenols will be apparent to those skilled in theart.

The polyamines (including diamines) used to prepare these salts maycontain any combination of primary, secondary, and tertiary aliphatic oraromatic amine groups. Preferred polyamines are those which when usedseparately as curatives for epoxy resins are highly reactive, providingrapid cures at room temperature. The

salts of this invention permit the use of such highly reactive amines inlatent one-component resin systems. 'Examples of these preferred aminesare 1,3-propanediarnine, ethylenediamine, 1,6-hexamethylenediamine,N,N-dimethyl-l,3-propanediamine, N,N-diethyl-1,3-propanediamine,diethylenetriamine, triethylenetetra-amine, and imino bispropylamine.Many other polyamines wi l be apparent to those skilled in the art.

A particularly useful curative is the 2: 1 salt of bisphenol A andtriethylenetetramine, a new composition of matter. Addition ofstoichiometric amounts of this salt to liquid epoxy resins such asdiglycidyl ethers of p,p'-isopropylidenediphenol (e.g. Epon 828, aliquid diglycidyl ether of bisphenol A with a molecular weight of 375and an epoxy equivalent of 192) gives semi-latent systems having shelflives of 3 to 4 weeks at room temperature and at least 6 months whenrefrigerated. On heating to 120 C. or higher, the crystals melt and/ ordissolve in the resin which then cures rapidly. Generally the resins gelwithin -15 seconds after the crystals dissolve. Since the preferredcuring agents allow so little time for diifusion, the salt must be veryfinely dispersed in the resin to obtain uniform cure.

Another preferred curative is the 1:1 salt ofN,N-dimethyl-1,3-propanediamine and2,4,4-trimethyl-2',4,7-trihydroxyfiavan, also a new composition ofmatter. When fine crystals are stirred into a liquid resin (e.g. Epon828) stable systems are obtained which undergo no significant prematurecure of the resin or settling of the curing agent after 8 months storageat room temperature. Rapid cure of the resin is obtained when theselatent systems are heated to 80 to 120 C. using as little as partscurative per hundred parts by weight resin in Epon 828, and even fastercures are obtained using parts per hundred parts by weight of this salt.

The shelf lives of the latent curing epoxy resin systems are mainlydependent on the stability of the salt curative, the crystal size, andthe solubility of the curative in the epoxy resins employed. Solubilityof the salt in the resins is difficult to measure, but an indicationofthis solubility can be obtained by measuring the solubility of the saltsin phenyl glycidyl ether, which is chemically similar to most epoxyresins. It has been found that salts which are useful in accordance withthe present invention have a room temperature solubility in phenylglycidyl ether of less than about 0.6 gm. per 100 ml. The pot lives ofsome epoxy resin systems containing the 1:1 salt of N ,N'-dimethyl-l,3-propanediamine and 2,4,4-trimethyl-2',4,7-trihydroxyfiavan areunexpectedly significantly longer than those obtained with other saltcuratives. While not wishing to be bound by any particular theory, itappears that the resin forms a gel on the surface of the individualcrystals of this particular curative, thus encapsulating the crystalsand preventing further reaction. Samples stored for long periods cure aswell as freshly prepared samples.

The crystalline phenol salt cnratives may be prepared in a number ofways. The preferred method consists of dissolving a polyphenol in asuitable hot solvent and adding either a stoichiomettric amount orexcess of a polyamine. The crystals that form on cooling are collectedby filtration, washed and dried. Alternately, a mixture of a polyamineand a polyphenol may be heated in a solvent and the crystals that formon cooling are collected, washed and dried. In some cases, thepolyphenols and polyamines may be heated together in the absence of asolvent and crystalline product obtained.

Many other polyamine polyphenol salts in addition to those given aboveare useful latent, heat activatable curing agents for epoxy resins,further examples being given in the accompanying examples, together withproperties of the resin systems. It will be obvious to those'skilled inthe art that this list is only representative of the many phenol aminesalt curatives which may be used and that many other similar salts couldbe cited.

The polyepoxides which may be made latent curing with the amine phenolsalt compositions of this invention are those organic compounds andresins, containing an average of more than one and generally more thanan average of about 1.5 oxirane groups per molecule, which can behardened with amines or polyhydric phenols. Examples of such epoxyresins include, among others, polyglycidyl ethers obtained from thereaction of dihydric or polyhydric alcohols with epichlorohydrin, forexample, resins made by condensing epichlorohydrin and glycerin to givediand tri-epoxides having a functionality of about 2.2 (e.g., Epon 812)and polyglycol polyepoxides such as the diglycidyl ether of polypropyene oxide (available commercially under the trade designation of D.E.R.736). Other examples include epoxidized polybutadiene and epoxidizedbutadiene-styrene copolymers.

Particularly useful resins are liquid polyglycidyl ethers of polyhydricphenols such as bisphenol A Which usually have slightly less than twooxirane groups per average molecular weight (for example Epon 828, orERL-2774). An example of a resin having more than two oxirane groups peraverage molecular weight are polyglycidyl ethers of phenol formaldehydenovolaks (for example those available commercially under the tradedesignation D.E.-N. 43 8). Still further examples of suitable reins arehigher molecular weight solid epoxy resins made by condensing bisphenolA and epichlorohydrin (e.g., Epon 1001).

Fillers, diluents, plasticizers, and modifiers may be incorporated inthe compositions of this invention. There is no deleterious effect onthe shelf life of these systems as long as the additives are notsolvents for the polyammonium phenate curatives.

The latent curing systems of this invention are useful in adhesives,laminating resins, potting compounds, and in other applications. Theresins using the preferred curatives can be shipped and stored, at roomtemperature, and applied to a substrate as a single component adhesive.Cure is then triggered when desired by applying moderate heat, generallyabove the C. to this resin, and preferably about C. to 150 C. Othersalts of invention may be used to provide increased pot life for inplant processing or may be shipped and stored at reduced temperatures.

The following examples, in which all parts are given by weight unlessotherwise indicated, will serve to further illustrate but not limit theinvention.

EXAMPLE I This example demonstrates the preparation of a crystallinepolyammonium phenate curative, the 2:1 salt of bisphenol A andtriethylene tetramine. Bisphenol A, 456 parts, was dissolved in theminimum amount of refluxing methanol and 146 parts of triethylenetetramine added. The mixture was cooled at room temperature andfiltered, The solid was washed with ether and dried to give 500 parts(83%) of salt, M.P. 138-142 C.

Calculated molecular composition for C H N O (percent): C, 71.7; H, 8.3;N, 9.3. Analysis (percent): C, 71.6, H, 8.2; N, 9.1.

The results of the use of this salt as a curative are given in TablesI-III.

To demonstrate that these salts may be used to cure thick castings, 30parts of the 1:2 triethylenetetraminc salt of bisphenol A was milledinto 98 parts of Epon 828 and 20 parts of the glycidyl ether of cashewnutshell oil, flexibilizer, on a roller mill. The mixture was degassedand cast into inch and 4 inch thick blocks, and cured at 140 C. for 20minutes to give clear well-cured blocks of resin. The top and bottomhardness of each of the cured blocks were determined to see if there wasany significant differences. The results, which are shown below.indicate that no appreciable settling of the salt occurs during thecuring and that these curatives can be used to prepare thick castings:

Rockwell M hardness A inch sample): Top 99 Bottom 102 Rockwell Mhardness inch'sample): Top 96 Bottom 92 EXAMPLE II fine crystals of thesalts into the resins or by milling the salts into the resins. Care mustbe taken to avoid heating the mixtures during the milling or mixingoperations in order to avoid premature cure. For example, 60 parts ofthe 2:1 salt of bisphenol A and triethylene tetramine was milled into195 parts of Epon 828 by giving the mixture two passes on a roller mill.This resin composition had a shelf life of about 4 weeks at roomtemperature but gelled in 1.7 minutes at 120 C. and gave clear wellcured samples after minutes. Samples kept at 40 F. are stable for atleast six months. The results obtained by incorporating other curativesin Epon 828 are given in Tables I-III, wherein a comparison with knowncuratives is also given. Other salts were prepared in a similar mannerand used as latent curing agents, results being given in Table III.

TABLE L--COMPARISON OF GEL TIMES OF LATENT CURATIVES AND CONVENTIONALCURA'IIVES IN EPON 828 Parts curative Curing per 100 temper- Gel time,

Curative parts resin ature, 0. minutes Shelf life, 25 0.

2:1 bisphenol A salt of triethylene tetramine 30 120 1. 7 3-4 weeks.Triethylenetetramine 10 120 3.0 1-2 hours.

1:1 N,N-dimethyl-1,3-propanediamine salt of 2,4,4- 120 2. 0 8 months ormore- Do-.. 30 120 1.2 6-8 months. N,N-dimethyl-l,3-propanediamlne- 10120 2. 5 1-2 hours. Dicyandiamide 6 145 15.0 6m0nths. Tri-Z-ethylhexoatesalt of 2,4,6-tris-(d1methy1am1n0- 10 120 10.0 12 days.

methyl) phenol (commercially available as Shell curative D") Borontrifluoride monoethylamine complex 5 120 16. 0 2-3 months.

TABLE II.ALUMINUM TO ALUMINUM OVERLAP SHEAR BOND STRENGTHS AT C. USINGERL-2774 EPOXY RESIN (U.S. MILITARY TEST MIL 1A 1509OD) Curative 2:1salt 01 bisphenol A and triethylenetetramine.

1:1 salt of N,N-dimethyl-1,3prop amine and 2,4,4-trimethy1-2,4hydroxyflavan.

Do Do anedi- 7-tri- Parts curative per 100 parts resin Cure cycle Bondstrength 10 min., 250 F., 122 0.. 3,000 p.s.i. (211 kgJcmJ). 20 60 min.,180 F., 83 C.---- 2,500 p.s.i. (176 kg./cm.

1 A glycidyl ether of bisphenol A having an epoxy equivalent weight of180-195.

TABLE III.POLYAMINEPOLYPHENOL SALT CURATIVES IN EPON 828 Salt CurativeRatio, Gel. Shelf Amine: Percent M.P., time, Temp Life, Amine Phenolphenol N C. Phr. 1 min. C 25 C.

Ethylenediamine Bisphenol A 1:1 8.8 99-108 25 2.0 120 1 day.Diethylenetriamine 2,4,4-trimethyl-2,4,7-trihy- 1:1 9. 8 117-23 33 3. 0130 1-2 weeks.

droxyflavan lflhexanediamine do 1:1 6. 6 150-3 30 2. 0 150 2 weeks.N,N-diethylethylenediamine do 1:1 6. 9 159-62 2. 5 140 1 week. 1,3-propanediamine do 1:1 7. 4 173-7 26 2. 0 120 Do.N,N-diethyl-ethylenediamine .do- 1:1 6. 7 142-7 30 15. 0 120 2 weeks.m-Phenylene-diamine. Resorcinol 1:1 81-85 18. 5 15. 0 120 3 hours.Ethylenediamine. 1,5-dihydroxynaphthalene 2:3 9. 8 150-4 18 10.0 135 1week. Diethylenetriamlne do 2:3 13. 4 120-3 18 10. 0 135 Do.

Do 2,2,4-trimethyl-4-(2,4-dihydro- 1:1 10. 9 85-90 40 4. 0 135 2 weeks.

xyphenyl) chroman Ethylenediamine do 1:1 8. 4 137-40 40 5. 0 120 1-2days. N,N-dimethyl-l,3-propanediamine "do 1 :1 7. 2 113-15 5. 0 100 2days. 1,6-hexanediamine 0,0-Biphenol 1 :1 9. 3 126-127 25 1 120 6 days.Ethylenediamine p,p-Biphenol 1:1 11. 2 196-202 20 1. 5 120 3 weeks.1,6hexanediamine do 1:1 7. 9 168-170 25 1. 5 120 Do. Ethylenediamine4,4-sulfonyl-diphenol 1:2 4. 9 218-221 25 19 120 12 weeks.Triethylenetetramine Tetrachloro-bisphenol A 1:1 10. 5 210-215 12 120Do.

1 Parts curative per 100 parts resin.

EXAMPLE IV 178-182 C. The other salts listed in Table III were similarlyprepared using various solvents such as acetone, ethanol, toluene, etc:

Calculated composition for C H N O (percent): C, 68.7; H, 8.5; N, 7.O.Analysis (percent): C, 68.7; H, 8.5; N, 6.9.

The results of the use of this salt as a curative are given in TablesI-III.

EXAMPLE III The salts of Examples I and II and other similarly preparedsalts were incorporated into resins either by mixing Five parts of the1:1 salt of N,N-dimethyl-1,3-propanediamine and2,4,4-trimethyl-2,4',7-trihydroxyflavan, 0-105p. crystals, was blendedwith 49 parts of the powdered solid epoxy resin, Epon 1001 (acondensation product of bisphenol A and epichlorohydrin having anaverage molecular weight of 875 and an epoxy equivalent weight of about450 to 525), to give a free flowing powder having indefinite shelf lifeat 25 C. Heating of this mixture at 120 C. for 10 minutes gave a cleartough hard cured epoxy resin.

EXAMPLE V 4,7-trihydroxyflavan to give a semilatent epoxy resin systemwhich had a shelf life of 1-2 weeks at room temperature. On heating to120 C. for 10 minutes, a tough flexible cured resin was obtained.

What is claimed is:

1. A polyphenate ammonium salt of N,N'-dimethyl-1, 3-propanediamine and2,4,4-trimethyl-2',4',7-trihydroxy- Fifty-four parts of a polyglycidylether of phenol formaldehyde novolak (D.E.N. 438) was warmed toapproximately 45 C. and 13 parts of the powdered 1:1 salt ofN,N-dimethyl-1,3-propanediamine and 2,4,4-trimethyl- 52',4',7-trihydroxyfiavan was stirred in and the mixture allowed to coolto room temperature. When this resin mixture was heated to 120 C. for 10minutes, a hard wellfiavan' R f Ct d cured resin was obtained. Thismixture had a shelf life e erences e of 1-2 weeks at room temperature,10 Baker 612 8.1., J. Chem. SOC. (1957) pp. 3060-4.

EXAMPLE VI HENRY R. JILES, Primary Examiner Sixty parts of anepichlorohydrin-glycerine condensate 1\/[ FORD A i t E i molecularweight 306, epoxy equivalent 150 (Epon 812) was mixed with 16 parts ofthe powdered 1:1 salt of 15 US. Cl. X.R. N,N-dimethyl-1,3-propanediamineand 2,4,4,trimethyl-2, 260-913, 837

